The influence of thermal degradation and the interruption time on the optical characteristics of InGaN multi-quantum-well (MQW) structures was examined. A series of 5-period In0.08Ga0.92N/In0.02Ga0.98N MQW samples with different final temperatures before cooling-down and with different interruption times during QW growth were grown on sapphire substrates by using metalorganic chemical vapor deposition. We carried out temperature-dependant photoluminescence (PL) and PL excitation measurements to elucidate the quantum efficiency and the origin of the emission, respectively. From a comparison of PL spectra and luminescence efficiency, we conclude that (1) high temperature ramping-up and exposure steps degrade the optical properties of QWs by thermal damage, (2) the InGaN QWs can be protected from thermal damage by a GaN capping layer, and (3) the interruption time during the QW growth somewhat degrades the optical properties of QWs.